Increasing choline availability of choline either by adding choline to the diet or by parenteral administration of choline, phosphorylcholine or lecithin only moderately increases brain choline levels without altering brain acetylcholine levels. In hippocampus and cortex but not in striatum, increased choline availability produces a significant reduction in acetylcholine turnover rates. Comparisons in the acetylcholine concentration and turnover rate of eight brain regions in each of seven strains of rats demonstrated interstrain differences as much as 40% in each measure. Large interstrain differences were also found in the acquisition of a conditioned avoidance response. However, no correlation among the strains was found between the response acquisisiton and either the acetylcholine concentration or turnover rate in any brain structure.